1. Field of the Invention
The present invention relates generally to radio systems and, more particularly, to systems and methods for automatic antenna matching for software-defined radio systems.
2. Description of Related Art
At the present time, there is tremendous demand for antennas with high efficiencies in very small form factors that fit inside ever-shrinking portable wireless devices like handsets and personal digital assistants. These antennas must cover a variety of frequency bands and support different wireless standards. Traditionally, antenna engineers have designed antennas for these applications using computationally-intensive full-wave electromagnetic simulation followed by long hours in the lab tweaking performance. It has become increasingly apparent that the requirements of software-defined radio (SDR) and its proposed successor, cognitive radio, will render this approach untenable.
One solution involves the use of automatic antenna matching techniques and devices that are widely used at lower radio frequencies (50 MHz and below). One area of effort has been to create these types of devices for use in commercial wireless and military communications systems, with particular concern for SDR systems. In a conventional antenna tuning system, the incident and reflected powers are coupled through a directional coupler in addition to two radio frequency (RF) power detectors, and then detected power levels are converted into digital domain; finally the return loss is computed by finding the difference between the two in digital domain. However, high accuracy ADCs are expensive, require moderate power and occupy significant space on a printed circuit board (PCB).